This invention relates to an ultrasonic surgical instrument. More particularly, this invention relates to a high-efficiency medical treatment probe for use in wound debridement.
Over the past 30 years, several ultrasonic tools have been invented which can be used to ablate or cut tissue in surgery. Such devices are disclosed by Wuchinich et al. in U.S. Pat. No. 4,223,676 and Idemoto et al in U.S. Pat. No. 5,188,102.
In practice, these surgical devices include a blunt tip hollow probe that vibrates at frequencies between 20 kc and 100 kc, with amplitudes up to 300 microns or more. Such devices ablate tissue by either producing cavitation bubbles which implode and disrupt cells, tissue compression and relaxation stresses (sometimes called the jackhammer effect) or by other forces such as micro streaming of bubbles in the tissue matrix. The effect is that the tissue becomes liquefied and separated. It then becomes emulsified with the irrigant solution. The resulting emulsion is then aspirated from the site. Bulk excision of tissue is possible by applying the energy around and under the target tissue to separate it from the surrounding structure. The surgeon can then lift the tissue out using common tools such as forceps.
The probe or tube is excited by a transducer of either the piezoelectric or magnetostrictive type that transforms an alternating electrical signal within the frequencies indicated into a longitudinal or transverse vibration. When the probe is attached to the transducer, the two become a single element with series and parallel resonances. The designer will try to tailor the mechanical and electrical characteristics of these elements to provide the proper frequency of operation. Most of the time, the elements will have a long axis that is straight and has the tip truncated in a plane perpendicular to the long axis, as shown in FIG. 1. This is done for simplicity and economic considerations. In almost all applications, whether medical or industrial, such an embodiment is practical and useful. However, in applications such as the debridement of burns, wounds, diabetic ulcers or ulcers induced by radiation treatments, the blunt straight probe has been shown to be less effective in removing the hard eschar buildup that occurs when the wound is healing. This eschar buildup must be removed so that the healthy tissue is exposed and allowed to close the wound to provide complete healing with minimal scar tissue formation. Also, the small diameter tip, since it is cannulated, has a small annular area with limits energy transmission into the wound. This extends the length of the procedure and causes operator fatigue and patient discomfort.
U.S. Pat. No. 7,931,611 discloses an ultrasonic wound debrider probe with a central bore coincident with the longitudinal axis. The proximal end of said bore communicates with a bore in the ultrasonic handpiece using methods well known to the art, such as a male/female thread combination. The probe is shaped such as to provide both a resonant frequency of operation in the range for which the electronic generator was designed and an amplitude of vibration at the distal face which is desired for proper tissue ablation. Such amplitudes have generally been shown to be in the range of 30 to 300 microns. Probe heads or ends as disclosed in U.S. Pat. No. 7,931,611 incorporate either a substantially symmetrical distal end or a distal end with a pronounced asymmetry. Each end has attributes that increase its effectiveness on varying tissue pathologies. Probe ends may be further modified to improve the liquid flow to the probe/tissue interface such as to reduce the bulk temperature rise of the tissue and prevent clogging of the liquid passageway. Probe ends may also be modified to produce energy directors that impart energy from the sides of the probes instead of only at the distal face of the probe. Such energy directors, when contacting skin or tissue, will increase volume of tissue treated per unit time and thereby reduce the operating time of the procedure. In one specific embodiment of U.S. Pat. No. 7,931,611, an ultrasonic medical probe has an elongate shaft which is formed integrally with a head portion having a distal end face oriented at least partially transversely to a longitudinal axis of the shaft. The shaft is provided with an internal longitudinal channel or bore extending to the end face. The end face is formed with an indentation communicating with the channel or bore at a distal end thereof, whereby liquid is guided over an extended surface of the end face relative to the channel or bore. The head portion may be enlarged in a transverse direction relative to the shaft. In that event, the end face has an elongated shape, while the indentation is elongate and forms a groove in the end face of the head portion. This groove may extend parallel to or in a length dimension of the end face.
A problem that sometimes arises with convention wound debrider and other ultrasonic surgical tools is that the irrigation channel or bore, which may be intermittently connected to a suction source, sometimes becomes clogged with tissue, thus reducing the effectiveness of irrigation and/or aspiration.